It changes the visuals, makes the interior compartment's navigation much easier but also adds a lot of realism features. It's flexible as you can take out the most realistic-demanding things to make it easier if you want.

Before trying this mod I didn't like SH4 at all, but after using it for only a little while I discover an entire new game.

Thank you @ Xenon for the nice review.
Was a little surprised that you left no comment in my thread after our conversation.
But now I have found this nice statement here from you.